Electromagnetic translating device



BEST AVAILABIE COPY A 29 1944. B. B. BAUER ELECTROMAGNETIC TRANSLATINGDEVICE Filed Feb. 7, 1941 2 Sheets-Sheet 1 fmszm Aug. 29, 1944. B BAUER2,356,810

ELECTROMAGNETIC TRANSLATINC- DEVICE Filed Feb. 7, 1941 2 Sheets-Sheet 2'mmax Patented Aug. 29, 1944 UNITED STATES v PATENT OFFICE y \f2,356,810 ELECTRQMAGNETIC TRANSISATING DEVICE Benjamin B. Bauer,Chicago, 111., assignor to S. N. Shure and Frances Shure, trustee, doingbusiness as Shure Brothers, a partnership 7 Application Febuary 7, 1941,Serial No. 377,855 I 17 Claims.

This invention relates to an electromagnetic translating device and moreparticularly to a phonograph recorder or reproducer.

(Cl. PIS-100.41)

entire vibratory system may be supported bev tween the pole pieces.

The recorders of the prior art have been generally characterized byheavy magnetic structures and relatively complicated vibratory systems.As a rule, the magnet has pole pieces of complex shape whose fabricationis inexpensive. The assembling of the entire deviceis inherentlyexpensive also.

The vibratory portions of the recorders of the art are eithermechanically complex and expensive or have undesirable vibratorycharacteristics.

The present invention provides a construction which is mechanicallysimple, ,yvhich has desir-' able and closely controllablecharacteristics in quantity production and which is sturdy. Oneimportant feature of the invention resides in the magnetic circuitconstruction whereby lightness, accuracy, economy and magneticeificiency are attained. Another important feature of the in ventionresides in the vibratory system. By vir.

\ tue of the construction of the vibratory system,

extreme mechanical simplicity and highly desirable vibratorycharacteristics result.

Mechanical simplicity in a vibratory device is highly desirable from atheoretical angle. Each discrete physical element in a system has itsown mass and elasticity. The more elements there are in a vibratorysystem, the greater the problem of resonance and transfer of energy fromone element to another. Y

The present invention in general contemplates a compact permanent magnethaving a ge eral block shape and provided with pole faces. fer to usecobalt bearing alloys as Alnico or similar alloys having high coerciveforce and relatively low remanence.

prefer to have the length of the magnet; i. e., the dimension along theinterior flux path, of the pre- In using such alloys, I

same order as the transverse dimension or (11- mensions and preferablyequal or even less than the transverse dimension. In such 'amagnet,

the projected pole area becomes substantial and comparable to theprojected area 'oithe remainder of the magnet. Thus full advantage oftheproperties of modern magnet materials is taken. The magnet materialsare generally hard so that they may be punched or stamped as desired;The

I a finished pole face is easily, accurately and eco 7 with its lengthas its The vibratory system consists of a combined armature and torsionspring piece and a rigid drive rod upon which aneedle may be mounted.

The construction is exceedingly simpleand concentrates substantially allof the elasticity'of the system within the one. armature and sprinpiece.

This is important since elasticity is one of the determinants oi thevibratory characteristics of the system. The elasticity and mass of thearmature and spring piece may be closely, controlled in production. Thisresults, in accuratecontrol of the overall characteristics as will beapparent later. .The physical coupling between the drive rod andarmature-spring piece isiaccomplished I in a simple but highly effectivemanner 'sothat for practical purposes the two may be considered as one.1 I. i

The entire device is noteworthy for the ease and lack of delicacynecessary for assembling. All parts to be assembled are firmly and"accurately retained in position and the final product isdependent upona few manufacturing tolerances rather than any assembly technique. In

one species of the invention, however, there is" I positioning the formof Fig. '6 is a sectional elevation alongline 6-8 of Fig. 5; I

Fig. '7 is an elevation from the rear; Fig. 8 isa perspective detail ofthe magnet and pole pieces of the modification;

Fig. 9 is a sectional plan view of a different modification; v I

Fig. 10 is a side elevation of the recorder of Fig.9;and v 1 Fig. 11is'a section on |lll of Fig." 10.

Referring to Figs. -1 to 4 inclusive, a magnet [0, preferably of somecobalt bearing alloy such as Alnico has two pole faces II and 12 groundsmooth. As shown, the magnet is rather squatshortest dimension and hasits pole faces at each end. Any desired shape or magnet may be provided.In general, the projected pole areas, here the areas or the faces,

- othe -to form 'an air gap limits.

are comparable to'the projected areas of the re- 'maining magnet sides.Disposed on the magnet I pole faces are soft iron orsoft steel framemembers l3 and 14 maintained in position by non,-

magnetic rivets IQ of brass, aluminum or the like.

The frame members are thin enough to be stamped or punched out of sheetmetal. By using hi hly permeable metalfor the pole pieces the fluxdensity therein may safely be higher than the normally lowdensity in themagnet proper.

Frame members l3.an d l4 extend beyond magnet It! to enclose the variousparts of the recorder;

While the frame members are hown as generally fiat pieces lying ingenerally parallel planes it is -to be understood that they may have anyde,-

sired shape and lie in any desired position relative to each otherdepending upon the mechanical details of construction. As shown here,frame members 13 and 14 extend away from magnet Ill for a distanceandare provided with blocks I 8 I and [9 of non-magnetic material.Non-magnetic rivets maintain blocks l8 and IS in position.

Blocks l8 and I3 may be of metal or not and preferably are rigid enoughso that a strong structure will result. Y

By having frame-members l3 and I4 extend beyond magnet 10, a region 2 isprovided between them in which the vibratory portion of the recorder maybe disposed. Adjacent region .2l, frame members l3 and. I have lateralextensions 22 and 23 bent out of the plane of the.

of extensions may be omitted and leave only one air'gap." 4

Operating within the twoair gaps are two portions 21 and 28 of a unitaryarmature whose center section 30 is extended to form a torsion tallpiece 3|. This combined; armature and spring is of elastic magneticmaterial and may be of soft iron or soft steel. -As shown in tl'iedrawings, the armature-spring member has a generally T-shape. While thearmature portions 21 and 28 are shown as equal and rectangular {it isclear that they may have any shape and length. Thus by tapering thearmature portions,

the stiffness and mass may be varied, In fact by controlling the shapeand dimensions of the armature and tail portions, any desired vibratorycharacteristic may be obtained. In any event,

this unitary piece is preferably a stamping and may be duplicated inproduction to within close slot 33 is preferably so dimensioned thatarmat e section 30 fits tightly therein. Thus the gr p between the twoparts extends over the entire opposing surfaces. Rivets 31 and 33extending transversely through the bifurcated rod end 75 providedin thepole pieces at the air gaps and 2,356,810 I r V andarmature section 30hold the two tightly is ;suitably apertured at an end together. Othermeans as welding or soldering may be provided. It is evident thereforethat rod 35 is supported for oscillation about its "1011- gitudinalaxis.

Drive rod 35 is preferably cylindrical and may be of. aluminum or anyother'metal, magnetic or non-magnetic. Irrespective of the length of lodinar'ily the only factor, from a-vibratory angle, present in rod 35 isinertia and thisis susceptible to close control in fabrication. The rodis simple and maybe made accurately in quantity. In

fact, by using aluminum or other light weight is material for the driverod and rivets 31 and 33,

the tolerances may be increased without ad-.

versely aifeoting the vibratory characteristics.

Rigid drive rod 35 is here shown as having substantial length andprovided with some support for its free end. This consists of a sleeve40 of rubber or other resilient material disposed around the free end ofrod 35 and supported in registering semi-circular channels ll in blocksI8 and I9. A v

This resilient support for the drive rod 35 permits the rod to oscillateabout its longitudinal axis. The sleeves 32 and 33 furnish a rigidsupport for the other end of the assembly comprise ing the drive M35 andthe elastic spring 30. 30 There is. no intermediate support. The springprovidestorsional compliance for the drive rod and, inaddition, sincethe spring is in the form of a flat leaf spring with its thin dimensionextending vertically and its wide dimension exvice shown in Fig. 1), itpossesses elastic compliance in a vertical direction and substantiallyno compliance in a horizontaldirection.

o v The free end of drive rod 35 is provided with 4 ah axial bore 42extending inwardly for a substantial distance and threaded toaccommodate *9 a lockingscrew 43. Transverse to bore 42 at an Pintermediate portion of rod 35 is a needle channel 45 into which aneedle 48 may be clamped by 45, screw 43. Needle 48 as a rule is ofhardsteel so that screw 43 does not bite intoit, Needle ll may passthrough anaperture 41 in bottom frame member M.

'The, cutter or recorder in use is normally dis- I 50 posed in theposition shown in Fig. 1 where frame in case of accidental dropping, theneedle point ordinarily strikes. first and drives the needle up to causeslippage. 'Io cushion the shock, a rub- 4 her or similar flexible pad 50is disposed below top frame piece l3 and above the needle bearingportion'of.the drive rod. i-Ience the cutter is protected againstdamage. Pad so also functions normally as a stop when i rting a needle.

Disposed between top and ottorn ,frame members l3 and H are spools 51and 58 carrying the voice current'coils 53. Where only one air gap andarmature section are provided,only one spool would be present. Thespools have narrow chanj nels 6|! through which armature sections 21 and28 are threaded and are disposed as close as 7 possible to the air gaps.I

Rubber sleeves El and 32 around drive rod;35 are thick enough to reachthesides-ogthe spools and may provide spool spacing; means as well as v*some non-resonant damping. Slots 83 may be rod 35, the torsionalelasticity is negligible. Or-

tending horizontally (in the position of the demember I3 is on top. As arule, the deviceielfim properties to magnet I0, has finished pole facesII and I2.

Soft steel pole pieces I3 and 74 are disposed against the opposite polefaces II and I2. Said pole pieces have extensions I5 and I5 and U-shapedend portions I6 and 76 terminating in pole tips TI, TI and I8, I8 andforming air gaps l9 and 80.

The pole pieces and magnet may be maintained intact in any manner and asshown are pressed together by a spring iJ-shaped frame member 82 ofsheet brass, aluminum or other non-magnetic metal. The arms 83 and 83'of the frame member may have retaining screws 84 passing through andengaging the pole pieces.

Frame member 82 has its bight portion 85 provided with a centrallydisposed generally semi-circular longitudinal channel 86'. This channelmay be formed by shaping the frame metal. Resting within said channel isthe drive rod portion of the vibratory system and consists of rod 90having spaced resilient sleeves BI and 92 with curved metal grips 93 and94 almost surrounding the rubber sleeves. The drive rod assembly ismaintained in position by spaced metal straps 95 and 96 extendingtransversely thereof and having the ends thereof rigidly fastenedto'frame member 82 by screws 91.. The object of the drive rod mountingis to provide a generally resilient mounting similar in properties tothe mounting between blocks 58 and I9 in Fig. 1.

One end 99 of drive rod 90 is bifurcated and grips a flat springarmature I extending upwardly .at right angles to said rod. The generalrod and armature construction is the same as in Figs. 1 to 'inclusive,except that armature I00 has a tongue I01 at the extreme end. As shownin Fig. 7, armature I00 extends through both air g ps l9 and 80. Driverod 90 has a transverse needle channel I03 in which a needle I04 may beclamped by screw I operating in axial threaded bore I06. Needle I04 mayextend through a suitable aperture I01 in frame channel 86;

While the drive rod mounting .may be relied upon to furnish a restoringforce to the armature. to position the same in the center of the airgaps, nevertheless additional means is preferred. This means may consistof a resilient strip 0 into which armature tongue Inf may 'be disposed.The ends of strip I I0 may be anextensions I32 and 833. Thus thearmature and spring member has a generally H-shape. The supports consistof screens I34 to E3! inclusive in spaced opposed pairs threaded in topand bottom frame members I3 and I4. The points of support for the springlateral extensions I32 and I33 may be'separated as widely as desired ormay Y In this'modification, asin that of Figs. 1 to 4,

the spring member provides torsional and vertical compliance andsubstantially no horizontal compliance.

In the various modifications, the drive rod has 3 been disclosed as arod of uniform cross-section throughout its effective length. Thisconstruction is the simplest to make and may sufi'ice fOr many purposes.However, in the event that torsional elasticity in the drive rod is tobe provided to a substantial degree or increased above that due touniform cross section then a departure from cross sectional uniformitymay be provided. Obviously the circular cross-section may be reduced toa small circular section or changed to a narrow rectangular section. Inother words, between the armature mounting part of the rod and needlecarrying part thereof a short length of the rod may be flattened, re-,duced to a smaller rod section or treated in some manner to introduce.a local torsional What is claimed is:

1. In an electromagnetic translating device, the combination of amagnetic circuit havingat least one air gap, a drive rod oscillatableabout its longitudinal axis, means consisting of a metallic torsionspring joined to said drive rod and extending from an end thereof in adirection longitudinally or said drive rod for supporting said end ofsaid drive rod and biasing said rod to a prechored by screws I H and H2engaging the pole pieces. Strip H0 may be and is preferably -adjustablymounted to permit accurate centering of'armature I00. Because strip IIOextends on both sidesof ton ue IOI, it is clear that the damping forceofthe strip is exerted both in compressipn and tension; I

Surrounding armature I00 is a. voice current coll H5 carried on a spooland firmly wedged in between the Us of thepole pieces.

Figs. 9 .to 11 inclusive show amodification of rubber or the like havincertain of the features of both preceding constructions. the magnetarid-pole piece construction follow lines of Figs. 1 to 4 inclusive. Thevibratory system differs both in the mounting and damping. Armatureportions I21 and I28 havea center section I30 extended to form a torsionpiece l3! and has lateral 75 determined at rest position fromwhich itmay be oscillated, said torsion spring possessing elastic compliance ina direction transversely thereof and 50 being substantially rigid in adirection normal to said direction of compliance, a substantiallyrigidsupport for said torsion spring at a portion thereof spaced from saidend of saiddrive rod, a support for said drive rod ata portion thereofspaced from said end of said drive rod, an armature carried by said rodand consisting of a fiat member extending transversely from said rodinto said air gap, at leastone voice current coil around said armature,and means on said rod between said support for said'rod and said end ofsaid rod joined to said torsion spring for supporting a stylus member ina pesition with its axis extending generally in the direction of saidtorsion spring transverse compliance.

2. in an electromagnetic phonograph translating device, the combinationof a magnetic circuit having at least one air gap, a drive rodoscillatable about its longitudinal axis, a unitary flat metallic memberhaving a resilient spring portion for sup porting and torsionallybiasing said rod and an armature portion extending into said air gap,said spring portionhaving elastic compliance i a direction normal to theplane of said flat member .and being substantially rigid in a direction'parallel to saidmlane, a voice current coil around compliance. 4

tensions being disposed toward said magnet, and an armature supported insaid air gap.

17. In an electromagnetic translating device, a permanent magnet havingpole faces on opposite sides thereof, pole piece fixed to said poleiaces respectively and extending beyond said magnet in spaced opposingrelation to each other,

each of said pole pieces having a pair of extensions bent toward theopposing pole piece at points spaced from each other and from saidmagnet to form a pair of air gaps between said extensions, and armaturemeans supported in said air gaps.

BENJAMIN B. BAUER.

. CERTIFICATE- 0F 'CLORRECTION. Patent No. 2, 56,810. s 9, 19M- BMJAMINB. BAUER.

I15 15 hereby e rtified' tht error appears in the ebeve numbered patentrequirin correqiion as fellows In the grant, li e 2, for the word"TRUSTEES" read -"-TRJSTEE--;111 1e 15 f or"es Trutees" read "Trustee";page L'fira-t olunin, line 8, for "ineipensive" read. --e x pens1ve=-;flin6 37, and second. column, line 50, ineert qiiotation marks before andafter the werd "A1n1e o" .page 5, second column, line-'5, for screensre'ada-acrewsarid that I said Lettere Patent should be read with tableeorrection therein that the same may co'niorm to the reeord of the casein the Patten t Offi B.

- sign'ed-a'hil sealec} fimsjaothfg'a 01 January, 4. DZ 1915.

Leslie Frazer (Send) I Acting Commissioner of Patents.

7 CERTIFICATE OF cpnREcnon. Patent No. 2, 56,810. ,Aug'ust 29, 191m.

' BENJAMIN B. BAUER.

It is hereby e rtified that error appears in the above nmnbered. patentrequiring correc ion as follows In the grant, line 2, for the word"TRUSTEES" read -'IHISI'EE--; line l'yjfor "es Trustees" read --Trusteepage l,'fire-t column, line 8, for "inexpensive" read--expens1ve-'-;fline 57, and second column, line 50, insert q xiotationmarks before and after the word "Alniovo";

.page5, second column, line 5, for "screens" read --sorews- -;.a1id thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the reeord of the case in the Patent Office.

- Signed me sealer; this 30th ea of January, 4;. D: 1915.

Leslie Frazer (Seal) Acting Commissioner of Patents.

